Systemic sclerosis (SSc) is an idiopathic connective tissue disease of unknown etiology that leads to debilitating and life-threatening fibrosis. Currently, no effective therapeutic or curative measures are available. We have recently made the novel observation of a significant increase in Insulin-Like Growth Factor Binding Protein-5 (IGFBP-5) expression in skin fibroblasts from patients with systemic sclerosis. We have further demonstrated increased IGFBP-5 in lung tissues of patients with pulmonary fibrosis and in primary fibroblasts cultured from these tissues. Furthermore, we have shown that IGFBP-5 is pro- fibrotic both in vitro and in vivo, suggesting that IGFBP-5 can initiate and perpetuate the fibrotic response. Collectively, our findings establish IGFBP-5 as a novel pro-fibrotic factor. We now demonstrate that IGFBP-5 induces reactive oxygen species (ROS) generation in primary fibroblasts. We also demonstrate trafficking of IGFBP-5 to caveolar and nuclear compartments. Furthermore, we show that IGFBP-5 induces expression and nuclear translocation of a novel DOK/IRS protein. We hypothesize that IGFBP-5 is a novel mediator of fibrosis that exerts its effects via a redox-sensitive signaling cascade. Moreover, IGFBP-5 trafficking and its pro-fibrotic activity are caveolin-dependent and involve induction of DOK5/IRS6 and nucleocytoplasmic shuttling of IGFBP-5 and DOK5/IRS6. Our specific aims are designed to test our hypothesis. We plan to 1) determine the role of redox-sensitive and -insensitive pathways in mediating the fibrotic effects of IGFBP-5, 2) determine whether the new DOK/IRS protein, DOK5/IRS6, induced by IGFBP-5, mediates its fibrotic effects, and 3) examine the role of nuclear compartmentalization of IGFBP-5 in its fibrotic activity. It is thus our goal to determine the mechanism by which IGFBP-5 induces fibrosis using a combination of in vitro, in vivo, and organ culture approaches. Completion of these aims will define the mechanism for the pro-fibrotic effects of IGFBP-5, and potentially identify novel therapeutic targets for the treatment of SSc and other fibrosing diseases. PUBLIC HEALTH RELEVANCE: The proposed studies will yield new insights into the mechanism of action of IGFBP-5, a novel mediator of fibrosis. Our studies will also generate new targets for the development of future therapies for the treatment of systemic sclerosis and other fibrotic diseases.